Overhead electric lines and conductors therefor



Jan. 17, 1956 a. BRAZIER ET AL OVERHEAD ELECTRIC LINES AND CONDUCTORSTHEREFOR Filed Aug. 8, 1951 2 Sheets-Sheet 1 JA Attorneys Jan. 17, 1956L. G. BRAZIER E'T AL 2,731,510

OVERHEAD ELECTRIC LINES AND CONDUCTORS THEREFOR Filed Aug. 8, 1951 2Sheets-Sheet 2 Inventors lea/[e fife/dens Braz/Pr- 2F Attorneys2,731,510 Patented Jan. 17, 1956 OVERHEAD Enters-ac MINES AND rrmnnnonLeslie Giddens Brazier, Hatchet, and VVilliam George Hawley, HinchleyWood, Esher, England, assignors to British Insulated Callenders CablesLimited, London, England, a British company Application August 8, 1951,Serial No. Claims priority, application Great Eritain Aug-M1129, 1956i 4Claims. (Cl. 174 114) This invention relates to overhead electrictransmission lines working at high voltages. The conductors of suchlines have to provide mechanical strength, conveyance of current andsuitable conditions for electric stress in the surrounding air. For thehigh voltages with which the invention is concerned the last mentionedrequirement determines the outside diameter of the conductor. This ismade such that the loss by electric discharge through the air is notexcessive.

For this purpose conductors havebeen designed consisting of two co-axialmetal parts separated by a layer of non-metallic material serving forspacing them apart. In this construction the tensile stress is takenmainly by the central part while both metal parts share in conductingthe current. The intermediate layer does not carry tensile stress ortake part in the conduction.

The present invention provides an improved conductor of the kind justreferred to and an overhead transmission system embodying it. In thisimproved conductor, the central member is a strand of wires of steel orother metal of high tensile strength with an outer part of wires. of ametal of good electrical conductivity, for example, aluminium wires. Onthis central. member is applied a continuous covering of paper, hemp orother filling material of suitable properties, as indicated hereinafter.The outer member of the conductor is a lhinavalled tube of metal of lowdensity and goon electrical conductivity, such as aluminium or analuminium rich alloy, having a smooth circular continuous outer surfaceand fitting closely on the filling material and forming a completeenclosure for the rest of the conductor structure.

The invention will now be more fully described with reference to theaccompanying drawings wherein Figure l is a perspective view of a shortlength of overhead line conductor made in accordance with the inventionand from which component layers have been cut back to show more clearlythe construction of the conductor,

Figure 2 is a perspective view of a short length of a second example ofoverhead line conductor made in accordance with the invention and fromwhich parts have been cutback to expose certain features of itsconstruction,

Figure 3 is an isometric view of a joint between two lengths of one formof our improved conductor, a central part of this figure being insection to show the construction of the conductor joint.

On referring to Figures 1 and 2 of the drawings, it Will be seen thatthe examples of overhead line conductor shown therein comprise a centralmember which comprises a central core 1 consisting of seven wires ofwhich six are laid up helically around a seventh to form a sevenwirestrand. These seven wires are of steel or other metal of high tensilestrength. Surrounding this central core 1 is a layer 2 of twelve wiresof metal of good electrical conductivity, preferably a light metal suchas aluminium. These twelve wires are laid up helically about the centralcore with a direction of lay opposite to that of the core wires. Aroundthis layer 2 of conductor Wires is a second layer 3 of eighteen similarwires which are laid up helically about and preferably in the oppositedirection to the wires of the underlying layer 2. The core 1 and itssurrounding layers 2 and 3 of conductor wires constitute the centralmember of our overhead conductor. It will of course be understood thatthe particular description that has been given above of the centralmember has been given by way of example and that central members ofother forms may be used. For instance, the core may con" se more thanseven wires of high tensile metal and the set rounding part (if any) ofthe central member may consist of a single layer of wires of .a metal ofgood conductivity or of more than two layers. The number of wires ineach layer may also vary from that shown when the diameter of the wiresin one layer differs from that of the wires in an adjacent lever.Surrounding the metallic central member (3, 2 and 3) of our improvedoverhead electric conductor is a continuous covering 4 of nonmetallicmaterial. Closely fitting the covering 4 and forming complete enclosurefor the rest of the conductor structure is a thin-walled tube 5 of alight metal or" good electrical conductivity, such as aluminium or analuminium rich alloy. This tube has a smooth circular continuous outersurface.

The covering lof non-rnetallic material between the metallic centralmember and the metal tube should be of relatively low density andcapable of undergoing the required bending without either offering greatresistance or suffering disintegration and should yet be sufficientlystrong to maintain the spacing of the two metal parts of the conductorand transmit the necessary mechanical forces between them, duringmanufacture, installation and service. This intermediate layer may, forinstance, be formed of helical lappings of paper tape, as shown forexample in Figure l where they are designated 6. It is preferred to usepaper or" substantial thickness, say 10 mils, to facilitate theoperation of building up the required thickness. The turns of each layerof paper may be applied with a substantial gap between them, say 25% ofthe width of the tape, care being taken that these gaps do not line upin adjacent layers of paper. In the example of conductor shown in Figure2, the layer 4 of filling material is formed by cords 7 of paper, hemp,or other material applied with a long lay side by side over the metalliccentral member and held in position with a binder 8 of tape applied witha short lay. It is emphasised that these two forms of intermediate layerare given only as examples of appropriate forms of construction,materials of other compositions and/or form and other methods ofapplication are available and will be recognised as suitable from theinformation given.

Several methods of forming the tubular outer member 5 are available. Itmay be extruded directly on the layer 4 of filling material so as to fitclosely thereon. It may be formed round the layer 4 by transverselybending to shape a strip of sheet metal and then welding the edges tocomplete the tube. In another method the tube may be formed separately,by extrusion or by bending and welding, or otherwise, so as to have aninternal diameter somewhat larger than the external diameter of the bodyon which it is to fit, namely, the covered central member.

This body can then be drawn into the tube and the latter then reduced bydrawing through a die to become a tight fit on the enclosed body.

In constructing the overhead line system, the conductor will besupported in the usual manner by clamps applied to its outer surface,that is, to the thin walled metal tube. In making joints, the inner andouter metal parts of the conductor will be joined separately by metaljoint sleeves applied over the adjacent ends and connected thereto. Toensure that the inner and outer metal parts of our improved conductorare put in good electric conductive connection at sufiiciently frequentintervals in the length of the line that appreciable potentialdifierences between them will not occur at intermediate points,conductive filling material, such as an intermediate tube or tubes ofmetal, will be placed between the inner and outer metal joint sleeves ateach conductor joint.

An example of a joint made between two lengths of our improved overheadconductor is shown in Figure 3. it

is made as follows: From the adjacent ends of the conductors shortlengths of the outer tubular parts 5 and 5 and of the layers 4 and 4 offilling material are removed and where, as shown, the metallic innermember includes an outer layer, or layers, of wires of a light metal ofgood electrical conductivity, parts of such layers are cut back in themanner shown in Figure l to expose short lengths of the cores 1 and land each of the layers 2 and 2' and 3 and 3. A sleeve 9 of suitablemetal, that is metal of high tensile strength such as steel, is slippedas a good fit over the two projecting ends 1 and 1' of the strandedmember and is compressed thereon in known manner so as to make effectiveconnection. If, as is shown, this sleeve 9 has when compressed on thecore, an external diameter approximating to that of the first layer ofwires 2, an opened split metallic tubular member 10 is laterallyinserted on the sleeve 9 and the adjacent exposed ends of the layers 2and 2 and closed down again. This split sleeve serves electrically toconnect the wires of layer 2 of one conductor length to those of thelayer 2 of the other conductor and to build up the diameter of the jointto that of the outer layers 3 and 3'. Over this split sleeve 10 islaterally applied a second split sleeve 11 serving to connect the wiresof the layers 3 and 3' electrically and to build up the joint to theexternal diameter of the outer tubular conductors 5 and 5. These arethen joined and the split sleeves compressed on to the wire conductorsand the core tube 9 by a sleeve 12 which was slipped over one of theends before the inner joint was made. This is now brought into positionover that joint so as to cover it and appropriate lengths of theadjacent parts of the tubes. It is then compressed in known manner tomake a good mechanical connection with these tubular ends. To facilitatethis connection the filling material 4 and 4' may be removed, as by atrepanning tool, from between the metallic inner member and the tube 5or 5' for a short distance and replaced by metal sleeves 13 and 13', asshown in Figure 3. This is preferably done before jointing the cores 1and l to avoid having to use a split sleeve. The sleeves 13, 13 may begrooved as at 14, 14 or otherwise formed to permit slight local inwardcompression of the tubular parts 5 and 5' and jointing sleeve 12 overit.

Instead of two separate sleeves 1t and 11 a single sleeve having astepped bore may be used. Where the inner joint sleeve 9 has an externaldiameter greater than the external diameter of the inner layer ofconductor wires this layer may be built up to the diameter of the sleeve9 and a single split sleeve be used to connect the conductor wires ofboth layers of one length to those of the other length and to build upthe inner joint diameter to that of the tubular conductor of eachlength. In place of one or more or the split tubes it) and 11, which arepreferably of aluminum, a wrapping of sheet metal or a binding of wiremay be used to effect a good electrical connection between the conductorwires surrounding the steel cores of the two lengths of overheadconductor and to build up the diameter of the core joint to the diameterof the tubular outer conductors.

The improved conductor, which has been found to be sufficiently flexiblefor the requirements of erection and service, has the advantage ofproviding a smooth circular form so as to avoid local electric stressconcentrations. This form also minimises wind resistance. The improvedconstruction also has the important advantage that the tubular outerpart forms a complete enclosure which is continuous over the jointsbetween lengths. This provides complete protection against the entry ofmoisture or gas which may corrode the internal strand or producedeterioration in the filling material. By appropriate choice ofmaterials the construction will provide a conductor of light weight fora given diameter and conductivity. Corrosion of the tubular outer partmay be retarded and its smooth surface maintained by the application ofa cor rosion resistant coating to its external surface.

What we claim as our invention is:

1. An overhead line conductor for high voltage electric powertransmission lines, comprising a steel cored aluminum wire strand havinga continuous covering layer of fibrous filling material surrounding saidstrand, and a tube having a thin, gas-impervious wall of metal selectedfrom the group consisting of aluminum and aluminum rich alloys of goodelectrical conductivity, said tube having a circumferentially continuouswall with a smooth circular continuous outer surface and fitting closelyon and being supported in spaced co-axial relationship to said strand bysaid fibrous covering layer and forming a complete gas-tight andwater-tight envelope for said fibrous covering layer and said strand.

2. An overhead line conductor for high voltage electric transmissionlines, comprising a steel cored aluminum wire strand, helical lappingsof paper tape disposed about said strand to form a supporting layer, anda thin walled tube of a metal selected from the group consisting ofaluminum and aluminum rich alloys of good electrical conductivity, saidtube having a circumferentially continuous wall with a smooth circularcontinuous surface and fitting closely on and being supported by saidsupporting layer in spaced co-axial relationship to said strand andforming a complete gas-tight and water-tight envelope for saidsupporting layer and said strand.

3. An overhead line conductor for high voltage electric transmissionlines, comprising a steel cored aluminum wire strand, a continuouscovering layer enclosing said strand and comprising cords of low densityflexible, strong, nonmetallic material applied side by side over saidstrand with a long lay, a binder of short lay disposed about andsecuring said cords applied with a long lay, and a thin walled tube of ametal selected from the group consisting of aluminum and aluminum richalloys of good electrical conductivity, said tube having acircumferentially continuous wall with a smooth circular continuousouter surface and fitting closely on and being supported by saidcovering layer in spaced co-axial relationship to said strand andforming a complete gas-tight and water-tight envelope for said coveringlayer and said strand.

4. An overhead line conductor for high voltage electric transmissionlines, comprising a central metallic member comprising a steel coredaluminum wire strand a continuous covering layer comprising non-metallicfilling material and surrounding said continuous covering layer athin-walled tube of sheet metal of low density and good electricalconductivity and having a single longitudinally extending seam welduniting the longitudinal edges of the sheet metal, said covering layersupporting said seam welded tube in spaced co-axial relationship to saidcentral member and said tube having a smooth circular continuous outersurface and fitting closely on the covering layer and forming a completegas-tight and Water-tight envelope for said covering layer and saidcentral member.

(References on following page) 5 6 References Cited in the file of thispatent FOREIGN PATENTS UNITED STATES PATENTS 503,044 Germany July 25,1930 1,664,100 Austin Mar. 27, 1928 243,209 Switzerland Dec. 2, 19461,981,890 Zapf Nov. 27, 1934 5 959,407 France Sept. 26, 1949 1,992,656Fletcher Feb. 26, 1935 3 Daniels Dec. 17, 1940 OTHER REFERENCES2,342,736 Herzog et 29, 1944 Ser. No. 193,918, Schmitt (A. P. 0.published May 2,534,935 Wagner Dec. 19, 1950 18,1943.

2,589,507 Noyes 1952 10 Electrical Engineering, July 1948, pg. 645.

